Multiple zone heating furnace



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A. W- LILLIENBERG MULTIPLE ZONE HEATING FURNACE Jan. 30, 1962 Filed July 28, 1958 Jan. 30, 1962 A. w. LILI u-:NBERG MULTIPLE ZONE HEATING FURNACE 2 Sheets-Sheet 2 Filed July 28, 1958 /N VEN TOR.'

ATTORNEYS.

United States Patent Giifiee 3,1ll906 Patented Jan. 30, 1962 3,019,006 MULTWLE ZONE HEATHNG FURNACE August W. Lillienberg, Chicago, Ill., assignor to Lindberg Engineering Company, a corporation of Illinois Filed July 28, 1958, Ser. No. 751,325 4 Claims. (Cl. 263-42) This invention relates to a multiple Zone heating furnace and more particularly to a furnace heated by combustion tubes and having `a plurality of zones therein.

lt is desirable in many cases to provide two or more heating zones in a furnace which are individually heated so that different temperatures can be maintained therein or so that one zone can be used for heating a partial load. In furnaces heated by combustion tubes this has heretofore been possible only by using different sets of tubes mounted at different heights in the side wall of the furnace. Such tubes must be assembled in the furnace at the time it is made and require substantially complete disassembly and rebuilding of the furnace for replacement. Furthermore, in Such installations the tubes are necessarily curved so that hot spots develop at the bends therein which cause the tubes to burn out more rapidly and which interfere with proper distribution of heat 'to the furnace charge. lt is one of the objects of the present invention to provide a multiple Zone heating furnace in which a plurality of zones in the furnace are effectively heated individually by straight tubes extending continuously through the furnace.

Another object is to provide a heating furnace in which straight tubes extending vertically through the furnace are supplied with parallel separate streams of primary fuel and `air and are provided with dimples or baille means in different vertical Zones of different tubes to create effective combustion in different Zones of the different tubes thereby to heat different zones in the furnace.

According to a feature of the invention the furnace may be provided with a tubular liner having openings in its central portion for air circulation and with upper and lower circulating fans for producing upper `and lower gas circulating streams.

The above and other objects and features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawings, in which:

FIGURE l is a vertical section through a multiple zone heating furnace embodying the invention;

FlGURE 2 is a partial section on the line 2 2 of FIG- URE l; and

FEGURE 3 is a view similar to FlGURE 1 of an alternative construction.

The furnace as shown in FGURE l comprises a vertically elongated tubular body indicated generally at 1li which may be formed by an outer shell 11 of sheet metal having a refractory lining 12 therein. The bottom of the furnace may be closed by a removable cover 13 or could, if desired, be closed by a permanent cover and the top is preferably closed by -a removable cover 14 through which the charge may be inserted in the furnace. The furnace may be charged with a plurality of loads indicated by the dot-dash lines 15 and 16 in different levels as, for example, by placing baskets containing parts to be heated in the furnace one above the other.

The furnace is heated by a plurality of combustion tubes arranged in different sets corresponding in number to the zones. In the furnace as illustrated wherein there are two Zones there are two sets of tubes, one indicated at '17 and the other at `13. As best seen in FIGURE 2, the tubes 17 are arranged alternately with tubes 13 in an annular series adjacent to the furnace wall so that they will surround the charge when it is placed centrally in the furnace as shown. Each of the tubes carries a burner 19 adjacent to its lower end which extends upward into the lower end of the tube to a level above the bottom of the tube and preferably adjacent to the inner floor of the furnace chamber. The burners for the tubes 17 are supplied with a primary fuel such as gas or an overrich mixture of gas and air incapable of complete combustion from a manifold 21. rl`he burners in the tubes l are similarly supplied with primary fuel from a manifold 22. The two manifolds are separately controllable so that either or both sets of tubes may be tired simultaneously.

In order to produce effective combustion in the tubes in different zones the tubes 17 are of smooth cylindrical configuration throughout approximately the lower half of their lengths and are formed with a series of inwardly projecting dimples or baffle means 23 spaced longitudinally and circumferentially around the tubes. ln similar manner the tubes 18 are formed with a series of inwardly extending dimples or baffle means 24 spaced longitudinally and circumferentially thereof throughout approximately the lower one-half of their lengths and are of smooth cylindrical configuration throughout the upper half of their lengths.

The tubes may be mounted in the furnace by inserting them through openings in the furnace top with the lower ends thereof extending through openings in the furnace bottom. Suitable sealing means indicated at 25 may be provided at the tops of the tubes to seal them tightly against the furnace top and to support the tubes and limit vertical downward movement thereof into and through the furnace.

In operation, assuming that the upper zone of the furnace only is to be heated, primarily fuel will be supplied through the manifold Z1 to the burners 19 and the tubes 17. The lower ends of the tubes are open so that air will rise through the annular space between the burners 19 and the inner walls of the tubes to pass in an annular stream around the stream of primary fuel issuing from the burner. Due to the smooth configuration of the lower halves of the tubes the primary fuel and air will mix to a very limited extent as they flow upward through the lower tube halves so that combustion will occur at a very slow rate, and the lower halves of the tubes 17 will be heated to a very limited extent. However, as the stream-s of primary fuel and air reach the dimpled upper portion of the tubes the dimples will cause progressive mixing and agitation of the primary fuel and air to increase the combustion at a rate determined by the size and spacing of the dimples. The upper halves of the tubes in which the dimples occur will, therefore, be heated to a maximum temperature and will radiate maximum heat on to the load in the upper basket 16.

In the the same manner when the tubes 1S are red by admitting fuel thereto from the manifold 22, the primary fuel and air will be mixed by the dimples or baffle means 24 in the lower half of the tubes so that maximum combustion will occur in the lower tube halves. The

-sarne temperature as desired.

ldimples are so related to the fuel and air flow and to the tube diameters that combustion will be completed by the time the fuel and air reach the upper smooth halves of the tubes so that the upper halves of the tubes 318 will be heated only by the residual heat remaining in the combustion gases and will achieve a temperature substantially lower than that of the lower halves of the tubes. In this way the lower halves of the tubes 18 may be heated to maximum temperature to provide maximum heat radiation on a charge in the lower basket and minimum radiation on a charge in the upper basket 15. By properly controlling the supply of fuel to the different sets of tubes the temperatures in the upper and lower zones of the furnace chamber may be accurately controlled to maintain the same temperature very closely or to maintain different temperatures as desired.

FIGURE 3 illustrates an alternative arrangement comprising an elongated tubular furnace body 26 having a removable top closure 27 for insertion of the load and a bottom closure 28. A series of tubes 29 dimpled throughout their upper halves and a second series of tubes 31 dimpled throughout their lower halves are diS- posed in annular series alternating with each other around the interior of the furnace in the same manner as the tubes 17 and 1S of FIGURES 1 and 2. The tubes 29 and 31 are separately supplied with primary fuel from manifolds 32 and 33 through burners 34 positioned above the open bottoms of the tubes in the same manner as the burners 19 of FIGURE 1.

In this furnace a tubular liner 35 is provided in the furnace radially inward from the series of tubes and the charge is adapted to be placed within the liner as, for example, in baskets, indicated by the dotted lines 36 and 3.7, stacked one above the other. For circulation of air lthe liner 35 is supported above the bottom of the furnace or may be formed with air circulating openings 3S therethrough as shown, and is formed in its central portion With additional air circulating openings 39.

For circulating the air or gas within the furnace two fans or blowers are provided. As shown, one fan 4l is carried by the lower closure plate 28 and is of the radial vaned blower type to draw air downwardly through the kliner 35 and the lower portion of the charge 36, circulate section, as shown, with its narrow point lying centrally adjacent to the openings 39 and is formed with openings therein through which the tubes 29 and 3i extend.

In operation with the furnace charged and with both fans 4l and 42 running, air will be circulated in the manner described and as indicated by the arrows. The

air circulated by the lower fan 41 will be heated primarily by the lower sections of the tubes 31 which are `the hot sections thereof, and will primarily circulate downwardly over the charge in the lower basket 36 so that its temperature is controlled mainly by the lower heated sections of the tubes 31. At the same time the air circulated by the fan 42 will be primarily heated by the upper hot sections of the tubes 29 and will return upwardly after entering the liner through the openings 39 to heat the charge in the upper basket 37. While there will inevitably be some intermingling of the air streams the effects will primarily be as described so that the charges in the different baskets can be heated by circulating air or gas at different temperatures or at the Applicant makes no claim to the broad concept of controlling the combustion rate -by supplying primary fuel Crt and air in separate streams to a combustion tube and obtaining progressive combustion thereof by means of dimples in the tube, this concept being more particularly disclosed and claimed in the copending application of John R. Duffy and August W. Lillienberg, Serial No. 382,686, filed September 23, 1953, now matured into Patent No. 2,849,220.

While two embodiments of the invention have been shown and described in detail, it will be understood that these are illustrative only and are not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

l. In a multiple zone heating furnace, a plurality of straight vertical combustion tubes for radiantly heating the interior of the furnace extending through the top and bottom walls of the furnace, each of the tubes being open at one end for ilow of secondary air thereinto a burner mounted within said one end of each of the tubes and defining with the tube coaxial passages for a primary fuel stream and a secondary air stream so that the primary fuel and secondary air will enter the tube in separate parallel streams, means for supplying the burner with a primary fuel containing insulllcient air for complete combustion, baille means in the tubes spaced longitudinally thereof for progressively agitating and promotting mixing of the primary fuel and air to effect progressive combustion in the tubes, the baille means in certain of the tubes spanning certain vertical zones only of the tubes corresponding to one vertical zone in the furnace and the baille means in others of the tubes spanning different vertical zones only therein corresponding to a different vertical zone in the furnace whereby the different tubes will effectively heat said different vertical zones in the furnace.

2. The furnace of claim l in which the burners for tubes in which the baille means lie in different vertical zones are supplied with fuel from separate means whereby heating of the different furnace zones can be separately controlled.

3. A multiple zone eating furnace comprising a tubular vertical furnace body having top and bottom walls, a plurality ofrstraight vertical combustion tubes extending through the top and bottom walls and distributed within the furnace body adjacent to the side walls thereof, each of the tubes being open at its bottom for flow of secondary air thereinto a burner mounted within the lower end of each tube and defining therewith coaxial passages for a primary fuel stream and a secondary air stream, means for supplying the burners with a primary fuel containing insutllcient air for complete combustion, certain of the tubes having baille means in their lower portions only and others of the tubes having baflle means in their upper portions only for progressively agitating and promoting mixing of the primary fuel and air to effect progressive combustion in said portions of the tubes thereby to effectively heat lower and upper lzones in the furnace, a tubular liner in the furnace lying within the ser-ies of tubes and having openings for gas circulation centrally of its length, and gas circulating units at the top and bottom ofthe furnace to create circulating gas streams through the liner and opening therein and respectively upwardly and downwardly over the tubes.

4. In a multiple zone heating furnace, a plurality of straight vertical combustion tubes for radiantly heating the interior of the furnace extending through the top and bottom walls of the furnace, each of the tubes being open at its bottom for flow of secondary air thereinto a burner mounted within the lower end of each of the tubes and dellning with the tube coaxial passages for a primary fuel stream and a secondary air stream so that the primary fuel and secondary air will enter the tube in separate parallel streams, means for supplying the burner with a primary fuel containing insufficient air for complete combustion, means in the lower ends only of certain of the tubes for progressively agitating and promoting mixing of the primary fuel and air to eect progressive combustion which will be completed in the lower ends only of said tubes, means in the upper ends of others of the tubes and at an elevation above the last named means for progressively agitating and promoting mixing of the primary fuel and air in the upper ends of said other tubes, the lower ends of said other tubes being smooth and unobstructed to minimize combustion therein.

References Cited in the le of this patent UNITED STATES PATENTS Kemp et al. Oct. 30, 1917 Herbst Dec. 27, 1932 Woodson Jan. 19, 1937 Woodson Nov. 22, 1938 Ogorzaly etal Nov. 25, 1952 McKeown iFeb. 12, 1957 Ipsen Feb. 11, 1958 Harris Oct. 27, 1959 

